Struct `Nothing`

struct Nothing

An empty syntax tree node that consumes no tokens when parsed.

This is useful for attribute macros that want to ensure they are not provided any attribute args.

# extern crate proc_macro;
#
use proc_macro::TokenStream;
use syn::parse_macro_input;
use syn::parse::Nothing;

# const IGNORE: &str = stringify! {
#[proc_macro_attribute]
# };
pub fn my_attr(args: TokenStream, input: TokenStream) -> TokenStream {
    parse_macro_input!(args as Nothing);

    /* ... */
#   TokenStream::new()
}

error: unexpected token
 --> src/main.rs:3:19
  |
3 | #[my_attr(asdf)]
  |           ^^^^

Implementations

`impl Clone for Nothing`

fn clone(self: &Self) -> Self

`impl Copy for Nothing`

`impl Debug for Nothing`

fn fmt(self: &Self, f: &mut fmt::Formatter<'_>) -> fmt::Result

`impl Eq for Nothing`

`impl Freeze for Nothing`

`impl Hash for Nothing`

fn hash<H: Hasher>(self: &Self, _state: &mut H)

`impl Parse for Nothing`

fn parse(_input: ParseStream<'_>) -> Result<Self>

`impl PartialEq for Nothing`

fn eq(self: &Self, _other: &Self) -> bool

`impl RefUnwindSafe for Nothing`

`impl Send for Nothing`

`impl Sync for Nothing`

`impl ToTokens for Nothing`

fn to_tokens(self: &Self, tokens: &mut TokenStream)

`impl Unpin for Nothing`

`impl UnwindSafe for Nothing`

`impl<T> Any for Nothing`

fn type_id(self: &Self) -> TypeId

`impl<T> Borrow for Nothing`

fn borrow(self: &Self) -> &T

`impl<T> BorrowMut for Nothing`

fn borrow_mut(self: &mut Self) -> &mut T

`impl<T> CloneToUninit for Nothing`

unsafe fn clone_to_uninit(self: &Self, dest: *mut u8)

`impl<T> From for Nothing`

fn from(t: T) -> T: Returns the argument unchanged.

`impl<T> Spanned for Nothing`

fn span(self: &Self) -> Span

`impl<T> ToOwned for Nothing`

fn to_owned(self: &Self) -> T
fn clone_into(self: &Self, target: &mut T)

`impl<T, U> Into for Nothing`

fn into(self: Self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of [From]<T> for U chooses to do.

`impl<T, U> TryFrom for Nothing`

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

`impl<T, U> TryInto for Nothing`

fn try_into(self: Self) -> Result<U, <U as TryFrom<T>>::Error>